Cathode ray tube



May 14, 1957 Filed June 22, 1951 w n 1 f.

N. BRQDERICK ETAL CATHODE RAY TUBE v 2 Sheets-Sheet 1 M @mm` @W JMM M ATTORNEYS May 14, 1957 N. E. BRODERICK ET AL 2,792,515

CATHODE RAY TUBE Filed June 22, 2 Sheets-Sheet 2 oo E ric

INVENTORS jg'zcholas Lrjode g1? zsovw 0 M ATTORNEYS ard JL MZM United States PatetitC CATHODE RAY TUBE Nicholas E. Broderick, East Paterson, and Edward J.

Llsoyicz, Newark, N. J., assignors to Thomas Elec- Itrorucs, Inc., Passaic, N. J., a corporation of New ersey Application June 22, 1951, Serial No. 232,966

2 Claims. (Cl. 313--82) This invention relates to cathode ray tubes, more particularly of the electrostatic focusing type.

As conducive to an understanding of the invention, it is noted that where the electronic stream of a cathode ray tube is focused by means of a magnetic field directed along the tube axis, the coil required for this purpose is bulky and relatively expensive and requires external leads and a source of power all of which adds to the cost of the installation in which the cathode ray tube is used.

Where, in order to dispense with the coil, electrostatic focusing is employed which involves the use of a focusing ring in the tube and a relatively high potential supplied from an external source, the tube base requires an additional prong to make the necessary connection and the installation in which the tube is used requires circuit connections from a high voltage source to the tube socket. Where such high potential is supplied by the same high voltage source of the installation that supplies the high voltage for the accelerating anode of the cathode ray tube, as such source of potential is generally extremely sensitive to overload, the resultant voltage drop may cause malfunctioning of the installation.

Where the electron stream is focused by means of such focusing ring which is generally positioned adjacent the accelerating anode of the cathode ray tube, if with a fixed focusing potential, a slight variation in spacing between the ring and the anode throws the tube out of focus, close manufacturing tolerances are required which greatly add to the cost of the cathode ray tube.

It is accordingly among the objects of the invention to provide a cathode ray tube which will focus without need for external focusing coils or an external connection to a source of power and such focusing will automatically be effected regardless of fluctuations in the line current, which tube does not overload the high voltage source of the installation in which it is used, may be made by mass production methods without need for close tolerances and may be incorporated in a conventional television set of the type normally requiring magnetic focusing, without the need for any redesign or rewiring of such set.

According to the invention the cathode ray tube has a focusing ring between its high voltage accelerating anode and the fluorescent screen of the tube, which ring is internally connected to an electrode of the tube which has a fixed potential applied thereto. More specifically the focusing ring is connected to the second or accelerating grid of the cathode ray tube which in conventional television sets has a potential thereon in the order of 300 volts.

In the accompanying drawings in which is shown onen of various possible embodiments of the several features of the invention,

Fig. 1 is a fragmentary longitudinal sectional view of the electron gun end of a cathode ray tube,

Fig. 2 is a transverse sectional view taken along line 2-2 o f Fig. l,

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Fig. 3 is a view similar to Fig. 2 taken along lino 3-3 of Fig. 1,

Fig. 4 is a view similar to Fig. 2 taken along line 4--4 of Fig. l,

Fig. 5 is a diagrammatic cross sectional vview of a cathode ray tube illustrating theelectron stream,- and Fig. 6 is a graph illustrating the relation of the focusing voltage to the spacing between the focusing ring and high voltage accelerating anode for optimum focusing.

Referring now to the drawings, the cathode ray tube desirably comprises an envelope 11, preferably of glass having a. fluorescent screen 12 (Fig. 5) at one end thereof. The other end of the tube has a base 13 with suitable prongs 14 for connection into a conventional socket (not shown).

Positioned in the neck 15 of the tube is an electron gun 16 which desirably comprises a cathode 17 having a heater 18 associated therewith to effect emission of electrons therefrom. Encompassing the cathode 17 is a control grid 19, which is desirably cup-shaped and has an aixal opening 21 through the end wall 22 thereof. Grid 19 is desirably mounted so as to be coaxial with neck 15 of the cathode ray tube, and suc-h mounting means may comprise a lead 23 aixed at one end as at 24 to grid 19 and at its other end 25 in the flange end 26 of an air evacuating tube 27, preferably of' glass, to which ange the end 28 of neck 15 of the cathode ray tube is affixed in conventional manner. A lead 29 desirably connects lead 23 to one of the prongs 14 in the base 13.

Afxed to grid 19 by means of lateral struts 32 anddesirably extending longitudinally through the neck 15 of the tube are a plurality of insulating supports 33, preferably of glass. Supports Y,33 mount a second grid 34, designated as the accelerating grid, which is longitudinally spaced from grid 19. Grid 34 also is desirably cupshaped and has an axial opening 35 through the end wall 36 thereof longitudinally aligned with opening 21 in end wall 22 of grid 19.

Also mounted on supports 33 is an accelerating anode 38 preferably sleeve-shaped as shown. Anode 38 extends longitudinally of grids 19 and 34 and is spaced from the latter. The outer end 39 of anode 38 desirably has an end wall or plate 41 with an axial opening 42 therein longitudinally aligned with openings 35 and 21.

Mounted on struts 43 affixed to the outer end 39 of anode sleeve 3S are a plurality of supports 44, also preferably glass rods which extend longitudinally in the neck 15 of the cathode ray tube.

The supports 44 carry an anode plate 45 which has an axial opening 46 therein aligned with axial openings 42, 35 and 21. Plate 4S is electrically connected to sleeve 38 by means of a metal strap 47 and the sleeve 38 is connected to the conductive coating 48 on the interior of the envelope by means of metal fingers 49 mounted on metal projections 51 extending laterally outward from the end 39 of the anode sleeve 38. Plate 45 also carries a plurality of strips 50 preferably of barium alloy which remove air from the tube when externally heated as by induction heating in conventional manner.

Positioned substantially midway between plates 41 and 45 is a metal focusing ring 54, which is desirably mounted on supports 44 by means of lateral struts 55 as shown in Fig. l. Ring 54 is electrically connected to one of the tube electrodes, preferably the grid 34 by' means of leads 56, 57 and 58, the lead 57 having a lead 59 connected thereto at one end and affixed in flange 26 as at 60, said lead 59 being connected by lead 61 to one of the prongs 14.

As the functioning of the cathode ray tube is well known to those skilled in the art, it will be described only tothe extent necessary for a clear understanding* ofthe invention and typical operating potentials will be given n with respect to a conventional 17 inch television tube.

The heater 18 is connected through base 13 to a sultable source of power to heat the cathode 17 `to an extent necessary to effect emission of electrons therefrom and the intensity of the electron stream from cathode 17 is regulated by grid 19 which controls the number of electrons that pass through the axial opening 21 in wall 22.

Grid 34, or the accelerating grid, has a fixed potential thereon of say 300 volts and serves to accelerate the electrons from the cathode and to converge them info a bundle of narrow cross section.This narrow portion of the ray bundle is usually referred to as the first cross over 64 and as shown in Fig. 5 occurs slightly beyond the -entrance end of the accelerating anode 33. The anode 38 as well as the anode plate 45 has a high potential, illustratively of approximately 12,000 volts, applied therto by means of an external connection to the anode button 65 which is electrically connected to the conducting coating 48 on the interior of the tube, said coating being engaged by the contact arms 49.

After the electron stream tends to converge at the first cross-over 64, shown in Fig. 5, the electron stream will again spread out as shown at 66. In order to have sharp focusing of the image to be seen on the fluorescent screen 12, it is necessary that the electron stream again cross-over at a point substantially against the fluorescent surface of such screen, indicated by the numeral 67. However, such second cross-over 67 is dependent both upon the voltage applied to the focusing ring 54 and the spacing between the plates 41 and 45.

From Fig. 6, which is a chartof optimum focusing based upon voltage and spacing, it can be seen that with a potential of say 1500 volts on focusing ring 54, indicated on the chart at 69, a spacing of .160 of an inch is required between the focusing ring 54 and plates 41 and 45 respectively for optimum focusing. If the spacing should vary by say plus or minus .0100 of an inch from the optimum spacing of .160 of an inch, the voltage required for optimum focusing at such spacing would be 850 volts for a spacing of .150 of an inch and 2100 volts for a spacing of .170 of an inch, as indicated by the numerals 71 and 72 on the chart. lt has been found, however, that such voltage range of 1250 volts is too great to afford satisfactory focusing near the extremes of voltage and as manufacturing conditions would generally cause variations in spacings in thc order of plus or minus .010 of an inch, it is apparent that satisfactory focusing would not be achieved with an initial fixed voltage of 1500 volts on the focusing ring.

With a lower focusing potential say of 50 volts, indicated at 73 on the chart, a spacing of .083 of an inch is required for optimum focusing. At such voltage if the spacing should vary even by .001 of an inch, which is highly probable if not inevitable with mass production methods, the voltage required for optimum focussing at .082 of an inch, indicated at 74, would be approximately volts and for a spacing of .084 of an inch, indicated at 75, would be approximately 80 volts. It has been found, however, that with low focusing voltages, although satisfactory focus is possible with a given spacing and a given voltage, even a slight variation in spacing will render the focusing with the same given voltage unsatisfactory.

From Fig. 6 it can be seen that with a potential of 300 volts on the focusing ring 54, indicated at 76 on the chart, a spacing of .100 of an inch is required between the focusing ring 54 Vand the plates 41 and 45 respectivelyfor optimum focusing.

If the spacing should vary by say plus or minus .0100 of an inch from the optimum spacing of .100 of an inch, the voltage required for optimum focusing at such spacings would be 200 volts for a spacing of .090 of an inch and 400 volts for a spacing of .110 of an inch as indicated by the numerals 77 and 78 on the chart.

It has been found that with a fixed potential of 300 volts on the focusing ring, highly satisfactory focusing will be achieved even with such .1010 of an inch variation in spacing and by reason of the leads 56, 57 and 58, which connect the focusing ring 541 to grid 34 which normally has a potential of 300 volts` applied thereto, such potential is also applied to the focusing ring 54.

With the construction above described, highly effective focusing is provided which will function satisfactorily even with substantially wide variations in manufacturing tolerances in the spacings between the focusing ring and the plates 41 and 54. inasmuch as the optimum voltage of 300 volts is available on the accelerating grid 34, no external circuit connections are necessary to provide such potential on the focusing ring and hence no external prongs are required on the tube base 13 for connection to the power supply of the installation in which the tube is used.

In addition to the highly desirable features above pointed, out, it is to be noted that the circuit herein automatically compensates the focusing for changes in potential on the accelerating grid 34 due to, for example, line tluctuations. Thus, if the potential on the accelerating grid 34 should drop to say 250 volts the potential on the focusing ring 54 would drop a corresponding amount. As a result, although the first crossover point would be retarded by reason of the drop .in the accelerating grid voltage, the second cross-over point 67 would still be against the fluorescent screen. This is because the difference in potential between the accelerating anode 38 and the focusing ring 54 would be increased and hence the electrons emitted from the accelerating anode wouldv move at slightly greater speed so that the second crossover would'occur slightly faster than it would have normally otherwise occurred and this second cross-over will again be substantially at the fluorescent screen.

The cathode ray tube above described, with its electrostatic self-focusing arrangement may be substitn-ted in a conventional television set for the cathode ray tube requiring magnetic focusing. All that would have to be done would be to disconnect the magnetic focusing coil from the circuit, or if such coil was included in the cir cuit arrangement of the set as a choke coil, for example, mrely to move such coil away from the cathode ray tu e.

As many changes could be made in the above construction, and many apparently widely different embodiments of this invention could be made without departing from the scope of the claims, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

Having thus described our invention, that we claim as new and desire to secure by Letters Patent of the United States is:

l. A cathode ray tube comprising an envelope having a fluorescent screen at one end and a neck at the other, an electron gun in said neck, said gun comprising a cathode, a filament to heat said cathode to effect emission of electrons therefrom, a grid adjacent said cathode on the screen side thereof to control the intensity of the electron stream,l a second grid adjacent said grid on the screen side thereof to accelerate the speed of the electrons emitted from said cathode, an anode between said second grid and said screen to further accelerate said electrons, a focusing ring between said anode and said screen for focusing said electron stream on said screen, a further anode between said focusing ring and said screen, said further anode being electrically connected to said first named anode within said envelope, said electrodes being spaced from one another by distances which effect a minimum spot size on said screen when saidv focusing ring is at the same potential as said second grid, and

electrical conducting means within said envelope directly connecting said focusing ring and said second grid together.

2. A cathode ray tube comprising an envelope having a fluorescent screen at one end and a neck at the other, an electron gun in said neck, said gun comprising a cathode, a filament to heat said cathode to effect emission of electrons therefrom, a substantially cupped shaped grid encompassing said cathode and having an end wall with an axial opening therein, a second grid longitudinally spaced from said first grid, said second grid having an end wall with an axial opening therein longitudinally aligned with the axial opening in said first grid, an anode sleeve longitudinally spaced from said second grid, said anode sleeve having an end wall at its outer end with an axial opening therein longi-tudinally aligned with the axial openings in said first and second grids, a focusing ring spaced from the end wall of said anode sleeve and longitudinally aligned therewith for focusing said electron stream upon said screen, a further anode electrode between said focusing ring and said screen, said further anode electrode being electrically connected to said anode sleeve within said envelope, said electrodes being spaced from one another by distances which effect a minimum spot size on said screen when said focusing ring is at the same potential as said second grid, and electrical conducting means within said envelope directly connecting said focusing ring and said second grid together.

References Cited in the tile of this patent UNITED STATES PATENTS 2,058,914 Rudenberg Oct. 27, 1936 2,070,319 Rudenberg Feb. 9, 1937 2,123,161 Schlesinger Iuly 5, 1938 2,137,352 Schlesinger Nov. 22, 1938 2,163,210 Wienecke June 20, 1939 2,191,415 Schlesinger Feb. 20, 1940 2,206,666 Epstein July 2, 1940 2,226,107 Schlesinger Dec. 24, 1940 2,227,034 Schlesinger Dec. 31, 1940 2,248,558 Schlesinger July 8, 1941 2,267,083 De Gier Dec. 23, 1941 2,276,320 Linder Mar. 17, 1942 2,363,359 Ramo Nov. 21, 1944 2,389,903 Hahn Nov. 27, 1945 2,452,919 Gabor NOV. 2, 1948 2,454,345 Rudenberg Nov. 23, 1948 2,461,743 Krahl Feb. 15, 1949 2,484,721 Moss Oct. 11, 1949 2,555,850 Glyptis June 5, 1951 2,673,305 Szegho Mar. 23, 1954 OTHER REFERENCES Industrial Electronics and Control by R. G. Kloetfler, copyright 1949, published by John W. Wiley & Co. See in particular page 453, ligure 2. 

